Method of fastening an implant to a bone and an implant therefor

ABSTRACT

An implant to be inserted into a bore or recess ( 22 ) of a bone, such as a jaw bone ( 23 ), comprises a radially expandable tubular member ( 12 ) which is preferably made from a helically wound string or wire, and a core member ( 13 ) to be positioned within the tubular member. The core member ( 13 ) may be moved axially in relation to the tubular member ( 12 ) so as to expand the tubular member radially, whereby the implant may be efficiently fastened. The core member ( 13 ) may be screwed into the outer tubular member ( 12 ) or into an anchoring member ( 11 ) arranged at the inner end of the recess ( 22 ). The implant is relatively easy to remove if such removal should become necessary by radially contracting the tubular member ( 12 ).

This application is the national phase under 35 U.S.C. §371 of PCTInternational Application No. PCT/DK98/00006 which has an Internationalfiling date of Jan. 7, 1998 which designated the United States ofAmerica.

The present invention relates to a method of fastening an implant to abone.

It is known to insert an implant in a bore or recess formed in a jawboneso that an artificial tooth may be mounted at the outer end of theimplant. The outer surface of the implant may have grooves or channelsformed therein so that the implant is efficiently fastened to thejawbone when bone tissue eventually grows into intimate contact with theouter surface of the implant. Infection may cause destruction of bonetissue in contact with the implant to such an extent that the implanthas to be removed from the jawbone. Such removal of the implant andreinsertion of a new implant is a complicated operation involvingremoval of bone tissue and enlargement the bore or recess in which thenew implant is inserted.

It is also known to insert an implant into the medullary cavity of abone. Such implant may for example include part of an artificialhipjoint. The insertion of known implants in medullary cavities normallyinvolves the use of so-called bone cement. Bone cement may decompose sothat the implant gets loose. Consequently, the patient has to undergo anew surgical operation.

The present invention provides a method allowing an improved and moreefficient fastening of an implant to a bone.

Thus, the present invention provides a method of fastening an implant toa bone, said implant comprising a core member and a radially expandableouter tubular member, which includes a helically wound elongated member,said method comprising forming a bore or recess in the bone, arrangingthe radially expandable tubular member in said bore or recess,positioning the core member so as to at least partly extend into theexpandable tubular member, releasably fastening the core member in thisposition in relation to the tubular member, and allowing bone tissue togrow into intimate contact with the outer surface of the tubular member.

When the tubular member has been inserted into the bore or recess formedin the bone the tubular member may be radially expanded, for example bymeans of the core member which is inserted into and fastened to thetubular member. This means that the outer surface of the tubular membermay be moved into engagement with the inner surface of the bore orrecess formed in the bone, whereby a good initial fastening of theimplant to the bone may be obtained. Furthermore, as explained below thetubular member may later rather easily be removed from the bone, ifnecessary.

The core member may be moved into and releasably fastened to the tubularmember in any suitable manner. As an example, outer thread-likeformations formed on the core member may be engaged with innertread-like formations formed in the tubular member.

An anchoring member may be arranged at the inner end at the bore orrecess in the bone and may be releasably connected to an adjacent end ofthe tubular member and/or the core member. Such anchoring member, whichis arranged at the inner end of the recess or bore may usually remain inthe recess or bore in case it is necessary to remove and replace thetubular member and the core member. A new tubular member and core membermay then be inserted in the recess and efficiently fixed when they arefastened to the already fixed anchoring member. The anchoring member mayhave any size and shape. Usually, it is preferred that the maximumradial dimension of the anchoring member exceeds that of the adjacentend of the tubular member.

In a preferred embodiment an outer thread-like formation formed on thecore member at the inner end thereof is engaged with an innerthread-like formation at an inner surface part of the anchoring member.The core member may then be moved axially in relation to the tubularmember by screwing the core member into the anchoring member.

The helically wound elongated member forming part of the tubular memberis preferably a string or wire. The windings of the helically woundelongated member may be in mutual abutting engagement. In this case thehelically wound elongated member may form a tubular member having asubstantially closed peripheral wall. Alternatively, adjacent windingsof the helically wound elongated member may be slightly spaced in theaxial direction of the tubular member. In order to obtain an unbrokenperipheral wall of the tubular member adjacent windings of the helicallywound elongated member may be interconnected by preferably thin,tearable wall parts.

When the implant is mounted in the bore or recess of the bone thetubular member may be inserted first and the core member may thereafterbe inserted into the tubular member. Preferably, however, the coremember is positioned within the tubular member prior to arranging thetubular member in the bore or recess. The core member may thereafter bemoved axially in relation to the tubular member.

The outer surface of the tubular member may have any suitable shape andmay, for example, be generally cylindrical. However, in order tofacilitate a possible later removal of the implant the outer surface ofthe tubular member may be tapered toward the inner end of the bore orrecess formed in the bone. As an example, the tapered outer surface ofthe tubular member may be frustoconical.

The outer surface of the core member and the inner surface of thetubular member cooperating therewith are preferably such that thetubular member arranged in the bore or recess formed in the bone isexpanded radially by moving the core member axially inwardly into theexpandable tubular member. As an example, the core member may comprisean outer, generally conical surface of the core member cooperating witha corresponding inner, generally conical surface of the tubular member.

The implant comprising an anchoring member, an outer tubular member, andan inner core member preferably forms a unit which is inserted into thebore or recess of the bone. Therefore, the anchoring member ispreferably releasably connected to the tubular member and/or the coremember prior to inserting said members into the bore or recess in thebone.

The bore or recess may, for example, be formed in a jawbone, and anartificial tooth may be fastened to the outer end portion of the coremember. Alternatively, the bore or recess may at least partly be formedby the medullary cavity of a bone. In the latter case part of anartificial hipjoint may be connected to the core member. When theimplant has been inserted in the medullary cavity of a bone theexpandable tubular member may be expanded as described above, wherebythe implant may be effectively fastened to the bone to such an extentthat the use of bone cement may become unnecessary. If an implant whichhave been mounted by the method according to the invention should getloose it would be possible later to further fastened the implant bytightening the thread connection between the core member and the tubularmember or the anchoring member so as to further expand the tubularmember into intimate contact with the inner walls of the medullarycavity. Such tightening would involve only a minor surgical operation.

The tubular member, the anchoring member, and/or the core member shouldbe made from physiologically tolerable materials which may be acceptedby the human or animal body in which it is to be used. Such materialsinclude titanium, plastic, and any other material conventionally usedfor implants.

If, for some reason, the implant has to be removed from a bone in whichit has been embedded for a shorter or longer period of time the coremember is first released from the tubular member and the tubular memberis subsequently removed from the bore or recess in the bone. Bone tissuemay have grown into depressions or grooves formed in the outer surfaceof the tubular member, whereby a strong adherence has been establishedbetween the tissue and the tubular member. However, because the tubularmember is at least partly formed by a helically wound elongated memberthe tubular member may be removed by pulling the outer end of theelongated member so as to unwind or straightened the elongated member.Thereby the removal of the tubular member is substantially facilitated.

Alternatively, the tubular member may be removed by arranging a toolalong the longitudinal axis of the tubular member, fastening a free endof the elongated member to the tool and rotating the tool about itslongitudinal axis so as to reduce the outer diameter of the tubularmember. When in this manner the tubular member has been removed from itscontact with the bone tissue it may easily be removed from the bore orrecess.

The present invention also provides an implant to be inserted in a boreor recess formed in a bone, said implant comprising a radiallyexpandable tubular member, a core member to be positioned within thetubular member so as to at least partly extend into the expandabletubular member, means for axially moving the core member in relation tothe outer tubular member, and means for releasably retaining the coremember in a selected position in relation to the tubular member. Thetubular member and the core member may then be provided with cooperatinginner and outer surfaces formed so as to cause a radial expansion of thetubular member when the core member is moved axially into the tubularmember so as to efficiently fasten the implant to the bone. The radiallyexpandable tubular member may comprise or be formed by a helically woundelongated member, such as a string or wire. Adjacent windings of thehelically wound elongated member may be in mutual abutting engagement ormay be slightly axially spaced. In either case adjacent windings may beinterconnected by wall parts which preferably are thin and tearable soas to allow removal of the tubular member by pulling the outer end ofthe elongated member so as to unwind and straighten it.

The moving and retaining means may comprise thread-like formations whichare formed on the core member and adapted to engage with innertread-like formations formed in the tubular member. The innerthread-like formations of the tubular member may be formed by thehelically wound elongated member which may also form outer thread-likeformations on the tubular member. As mentioned above, the implant mayfurther comprise an anchoring member and means, such as thread means,may be provided for releasably connecting the anchoring member to theinner end of the tubular member and/or the core member.

It should be understood that the outer tubular member need notnecessarily be made from a helically wound elongated member, but couldhave any shape allowing a certain radial expansible thereof. It is alsoenvisaged that it is not strictly necessary that the tubular member isradially expansive. Thus, when the implant comprises an anchoring memberas described above the tubular member could have an inwardly taperedouter surface which could be moved into contact with the inner wall ofthe bore or recess when the tubular member is connected to and movedinwardly in relation to the already fixed anchoring member.

The invention will now be further described with reference to thedrawings, wherein

FIG. 1 is a side view of a first embodiment of the implant according tothe invention,

FIGS. 2-4 illustrate the various parts of the implant,

FIGS. 5 and 6 illustrate how the outer tubular part of the implant maybe removed from a jawbone,

FIG. 7 is a sectional view illustrating a second embodiment of theimplant according to the invention mounted in a jawbone,

FIGS. 8-11 are sectional views illustrating various steps in mountingthe implant in the jawbone,

FIG. 12 is a sectional view of a third embodiment of the implantaccording to the invention mounted in a jawbone,

FIGS. 13-15 are sectional views illustrating various steps of mountingthe implant,

FIG. 16 is a sectional view of a fourth embodiment of the implantaccording to the invention,

FIGS. 17-19 are sectional views illustrating the various steps ofmounting the implant in a jawbone,

FIGS. 20 and 21 are fragmentary sectional views showing differentcross-sectional shapes of the elongated member and how adjacent windingsare interengaging,

FIG. 22 is a cross-sectional view showing an implant according to theinvention mounted in the medullary cavity of a bone, and

FIG. 23 illustrates how the implant shown in FIG. 22 may be fastened.

FIG. 1 shows an implant for fastening an artificial tooth 10 and to bemounted in a bore or recess formed in a jawbone, for example a cavityfrom which the root of a natural tooth has been removed. The implantcomprises and inner anchoring member 11, a tubular member 12, a coremember 13, and an abutment member 14 to which the artificial crown of atooth 10 may be fastened.

In the embodiment shown the anchoring member 11 has the shape of aspherical segment and is releasably fastened to the inner end of thetubular member 12. The tubular member 12 is formed by a helically woundwire or string and is tapered towards the anchoring member 11. Thewindings of the wire or string define inner and outer threads on thetubular member.

The core member 13 has a tapered conical shape which is complementary tothe inner surface of the tubular member 12. Thus the outer surface ofthe core member 13 has thread-like formations which may engage with theinner threads of the tubular member 12. The core member 13 also has ahead 15 with a radially extended collar 16 and an axially extendingthreaded bore 17. The head 15 of the core member 13 also defines anouter frustoconical surface 18 which is received in a recess 19 formedin the abutment member 14 having a frustoconical surface which iscomplementary to the surface 18. The abutment member 14 also has athrough axial bore 20 for receiving a fastening screw 21 which mayengage with the threaded bore 17 of the core member head 15 so as tofasten the abutment member 14 to the core member 13.

The implant comprising the anchoring member 11, the tubular member 12,and the core member 13 may be inserted in a recess or bore formed in ajawbone where an artificial tooth should be mounted. When the implanthas been inserted in the jawbone the tubular member 12 may be expandedradially by screwing the core member 13 into the tubular member wherebythe outer surface of the tubular member may be moved into tightengagement with the outer peripheral wall of the bore or recess formedin the jawbone. The abutment member 14 may then be fastened to the coremember 13 by means of the screw 21, and finally, the artificial toothcrown 10 may be fastened to the abutment member 14 in a conventionalmanner.

FIGS. 5 and 6 illustrate how an implant of the type shown in FIGS. 1-4may be removed from a recess 22 in a jawbone 23 in which it has beenmounted for a certain period of time so that bone tissue has grown intointimate contact with the outer surface of the tubular member 13. Asshown in FIG. 5, the recess 22 in the jawbone may be located between apair of adjacent natural teeth 24. When the abutment member 14 has beenremoved by unscrewing the fastening screw 21 the core member 13 may bescrewed out of the tubular member 13. Thereafter the outer free end 25of the wire or string forming the tubular member 13 may be fastened to arod-shaped tool 26 which has been inserted axially into the recess 22and which has a handle 27 at its outer end. By rotating the tool 26about its axis in a direction indicated by an arrow 28 the tubularmember 12 may be contacted radially as illustrated in FIG. 6 and therebyloosened from the bone tissue forming the peripheral wall of the recess22. Now, the tubular member 13 may be released from the anchoring member11 and removed. The anchoring member 11 may remain in its position andmay be used when a new implant is inserted into the recess 22.

FIGS. 7-19 illustrate further embodiments of implants of the typeadapted to be mounted in a jawbone in order to fasten an artificialtooth crown to the jawbone 23, and in the following description partscorresponding to the parts shown in FIGS. 1-6 will be designated thesame reference numerals.

In the embodiment shown in FIGS. 7-11 the anchoring member 11 which ismounted at the inner end of the conical or tapered recess or bore 12 hasa substantially cylindrical peripheral wall. The peripheral wall of theanchoring member 11 is provided with inner and outer threads 29 and 30,respectively. As shown in FIG. 8 the tubular member 12 is inserted intothe recess 22 in a radially contracted, substantially cylindricalcondition, and the inner end of the tubular member 12 is positionedwithin the anchoring member 11. When a tubular member 12, which isformed by a helically wound wire or string, is released the resiliencyof the tubular member causes a radial extension of the tubular member soas to move the outer surface thereof into close contact with the innerthreads 29 of the anchoring member 11 and the inner walls of the recess22, respectively, as illustrated in FIG. 9. The core member 13 comprisesan outer tubular core element 13 a having outer threads and an innercore element 13 b fittin into the tubular element 13 a. As shown in FIG.10, the outer tubular element 13 a may be screwed into engagement withthe inner surface of the tubular member 12, whereby the tubular membermay be further radially extended, and the inner core element 13 maythereafter be inserted into the bore of the tubular element 13 a, andthe inner free end of the element 13 b is provided with outer threads 32which may engage with the inner thread-like formations formed by theinner end of the tubular member 12 which is located within the anchoringmember 11. An enlarged head 33 at the outer end of the inner coreelement 13 b has an axial threaded bore 34 formed therein, and theabutment member, which is adapted to receive an artificial tooth crown(not shown) has a threaded neck 35 which may be screwed into thethreaded bore 34 whereby the abutment member 14 is fastened to the innercore element 13 b.

FIGS. 12-15 illustrate a modification of the embodiment shown in FIGS.7-11. In the embodiment shown in FIGS. 12-15 the core member 13 is asingle unitary part, which is not divided into two separate elements asshown in FIGS. 7-11. Otherwise the two embodiments are alike.

The embodiment of the implant shown in FIGS. 16-19 does not comprise ananchoring member and, consequently, the core member 13 does not have acylindrical inner end portion with threads 32 to cooperate with theanchoring member. In all other respects the embodiment shown in FIGS.16-19 substantially corresponds to that shown in FIGS. 12-15.

Adjacent windings of the helically wound string or wire from which thetubular member 12 is made is preferably in close mutual contact in themounted condition of the implant in order to prevent bone tissue fromgrowing into the inner space of the tubular member. FIGS. 20 and 21illustrate different cross-sectional shapes of the string or wireallowing such close contact. The helically wound wire or string 36 shownin FIG. 20 defines inner and outer surface parts 37 and 38,respectively, which may be in mutual abutting contact whether or not thetubular member 12 is more or less radially expanded. In the embodimentshown in FIG. 21 the wire or string has a channel 39 and a diametricallyoppositely extending projection or ridge 40 such that the ridge 40 mayfit into the channel 39 of an adjacent winding of the wire or string 36.

FIG. 22 shows a longitudinal section of a thighbone 41 from which an endportion 42 has been cut off so as to expose the medullary cavity of thebone. An implant 43, which may be of any of the embodiments describedabove, is inserted into and fixed in the medullary cavity by expandingthe outer tubular member 12 in a manner previously described. The outerend of the core member 13 of the implant may be formed as a hip jointpart 44 or such artificial hip joint part may be fastened to the coremember 13 in any suitable manner. A complementary artificial hip jointpart (not shown) may in a similar manner be mounted to the hipbonewhereby a natural hip joint may be replaced by an artificial one.

As illustrated in FIG. 23 the helically wound tubular member 12 which ismounted in the medullary cavity of the thighbone may be further expandedgradually and fastened or contracted radially so that it may be removed.For this purpose the core member 13 may comprise a rotatable, axiallyextending actuating member 45, which may be rotated by a suitable toolsuch as a screw driver.

It should be understood that various embodiments and modifications ofthe embodiments shown could be made without departing from the scope ofthe present invention. Thus, features and parts disclosed in the variousdrawings may be combined or interchanged.

What is claimed is:
 1. A method of fastening an implant to a bone, saidimplant comprising a core member and a radially expandable outer tubularmember, which includes a helically wound elongated member defining anouter peripheral surface of the tubular member, said method comprisingforming an inwardly tapering bore or recess in the bone, arranging theradially expandable tubular member in said bore or recess, moving thecore member into the tubular member so as to expand the tubular memberradially, releasably fastening the core member in relation to thetubular member in a position in which the tubular member is in contactwith walls defining the bore or recess, and allowing bone tissue to growinto intimate contact with the outer surface of the tubular member.
 2. Amethod according to claim 1, wherein outer threadlike formations formedon the core member are engaged with inner thread-like formations formedin the tubular member.
 3. A method according to claim 1, furthercomprising arranging an anchoring member at the inner end of the bore orrecess in the bone and releasably connecting the anchoring member to anadjacent end of the tubular member and/or the core member.
 4. A methodaccording to claim 3, wherein the maximum radial dimension of theanchoring member exceeds that of the adjacent end of the tubular member.5. A method according to claim 3, wherein an outer thread-like formationformed on the core member at the inner end thereof is engaged with aninner thread-like formation at an inner surface part of the anchoringmember.
 6. A method according to claim 3, wherein the anchoring memberis releasably connected to the tubular member prior to inserting saidmembers into the bore or recess in the bone.
 7. A method according toclaim 1, wherein the elongated member is a string or wire.
 8. A methodaccording to claim 1-7, wherein the windings of the helically woundelongated member are in mutual abutting engagement.
 9. A methodaccording to claim 1-8, wherein adjacent windings of the helically woundelongated member are interconnected by tearable wall parts.
 10. A methodaccording to claim 1-9, wherein the core member is positioned in thetubular member prior to arranging the tubular member within the bore orrecess.
 11. A method according to claim 1-10, wherein the outer surfaceof the tubular member is frustoconical.
 12. A method according to claim1, wherein the bore or recess is formed in a jawbone, and an artificialtooth is fastened to the outer end portion of the core member.
 13. Amethod according to claim 1, wherein the bore or recess is at leastpartly formed by the medullary cavity of a bone.
 14. A method accordingto claim 13, wherein part of an artificial hip joint is connected to thecore member.
 15. A method according to claim 1, wherein the tubularmember, the anchoring member, and the core member are made from aphysiologically tolerable material.
 16. A method according to claim 1,further comprising releasing the core member from the tubular member andsubsequently removing the tubular member from the bore or recess.
 17. Amethod according to claim 16, wherein the tubular member is removed bypulling the outer end of the elongated member so as to unwind orstraighten the elongated member.
 18. A method according to claim 17,wherein the tubular member is removed by arranging a tool along thelongitudinal axis of the tubular member, fastening the outer end of theelongated member to the tool and rotating the tool about itslongitudinal axis so as to reduce the outer diameter of the tubularmember.
 19. A method according to claim 1, wherein the anchoring memberis releasably connected to the core member prior to inserting saidmembers into the bore or recess in the bone.
 20. An implant to bepositioned in a bore or recess formed in a bone, said implantingcomprising: an outer radially expandable tubular member which includes ahelically wound, elongated member defining an outer peripheral surfaceof the tubular member, a core member to be positioned within the outertubular member so as to at least partly extend into the expandabletubular member from an outer end thereof, means for axially moving thecore member in relation to the outer tubular member so as to expand thetubular body radially, and means for releasably retaining the coremember in a selected position in relation to the tubular member, in itsexpanded condition the outer tubular member being tapered towards aninner end opposite to said outer end.
 21. An implant according to claim20, wherein outer thread-like formations formed on the core member areadapted to engage with inner thread-like formations formed in thetubular member.
 22. An implant according to claim 20 further comprisingan anchoring member, and means for releasably connecting the anchoringmember to the inner end of the tubular member.
 23. An implant accordingto claim 22, wherein the minimum radial dimension of the anchoringmember exceeds that of the inner end of the tubular member.
 24. Animplant according to claim 22 or 23, wherein outer thread-likeformations formed on the core member are adapted to engage with innerthread-like formations at an inner surface of the anchoring member. 25.An implant according to claim 22, wherein the anchoring member is anut-like member.
 26. An implant according to claim 20, wherein theelongated member is a string or wire.
 27. An implant according to claim20, wherein the windings of the helically wound elongated member are inmutual abutting engagement.
 28. An implant according to claim 20,wherein adjacent windings of the helically wound elongated member areinterconnected by tearable wall parts.
 29. An implant according to claim20, wherein the outer surface of the tubular member is tapered towardthe inner end when the tubular member is in its unexpanded condition.30. An implant according to claim 29, wherein the outer surface of thetubular member has a conical or frustoconical shape.
 31. An implantaccording to claim 20, wherein the implant is adapted to be inserted ina bore or recess formed in a jawbone, the outer free end portion of thecore member having means for fastening an artificial tooth thereto. 32.An implant according to claim 20, wherein the implant is adapted to beinserted into a bore or recess at least partly being formed by themedullary cavity of a bone.
 33. An implant according to claim 32,wherein the implant comprises part of an artificial hip joint connectedto or forming part of the core member.
 34. An implant according to claim20, wherein the tubular member, the anchoring member, and the coremember comprise a physiologically tolerable material.
 35. An implantaccording to claim 34, wherein the tubular member is made from titaniumwire.
 36. An implant according to claim 20, wherein the core member hasa shape tapering toward an inner end thereof.
 37. An implant accordingto claim 36, wherein the tubular member has a substantially cylindricalshape in its unexpanded condition.
 38. An implant according to claim 20,further comprising an anchoring member and means for releasablyconnecting the anchoring member to the inner end of the core member.